In general, the demand for smaller, yet more powerful, electronic circuit modules, which have more features or capabilities and greater component density than their predecessors, has been increasing. This is especially true in the case of PWBs configured as power converters that are often employed in power supplies. A power converter is a power processing circuit that converts an input voltage waveform into a specified output voltage waveform. In many applications requiring a DC output, switched-mode DC/DC power converters are frequently employed to an advantage wherein both high conversion density and converter efficiency are key design requirements.
In these devices, and PWBs in general, electrical connections between the various layers and components are typically accomplished with the use of vias, which, as is well known, are openings or holes that extend through the board and that typically have a conductive material, such as solder, therein. In conventional vias, the conductive material covers the entire interior wall of the via. In such structures, any conductive trace that the via intersects is electrically connected to every other conductive trace that also intersects that same via. Thus, only one electrical connection can be made for each via, which requires multiple vias to make the multiple connections for PWB's having a high component density. For example, in technologies that implement core-on-board transformer technologies, many vias are required to make the necessary connections to various field effect transistors (FETs), transformers and inductors.
As such, these vias consume valuable board space. When the board layout is complex and includes many electrical components, the number of vias (and the concomitant amount of board space consumed by them) increase dramatically. When a larger number of vias are required for the board layout, it becomes very difficult for manufacturers to keep the board dimensions and layout within specified design requirements and yet still make the number of electrical connections that are required for the desired operation of the device. In addition, the typical via is a through-hole via, and since it goes through all layers, routing of conductive traces on internal layers becomes an issue. Moreover, the electronics industry is quickly moving to on-board technology where more, if not all, of the components are formed directly on or within the board itself. This advancement in technology reduces the number of separate components that are soldered directly to the board. Thus, it is becoming ever more imperative that all space of the board is efficiently utilized.
In an attempt to increase the amount of space on the PWBs, manufacturers have turned to a couple of processes. One such process is a controlled depth via. In this process, a hole is drilled to a certain depth sufficient to connect a given number of conductive metal layers together. The board can then be drilled in a similar fashion on the reverse side. While this controlled depth technique allows for a couple of separate interconnections, it is time consuming, not reliable, produces poor manufacturing yields, and thus, is costly to achieve. Additionally, it does not provide an adequate decrease in overall number of vias that must be drilled in the PWB.
Another process employed by the industry is the buried via technique where a partial via is made in two or more PWB conductive layers of the board. The layers are electrically connected together, and then they are covered by subsequent PWB layers. Internal layers are drilled and plated for a buried via or laminated, drilled, and plated for a buried or through hole via connecting more than two conductive layers. This has basically the same effect as the controlled depth technique as above, but unfortunately suffers greater disadvantages in that this process is even more time consuming and more costly than the controlled depth technique.
Accordingly, what is needed is PWB with an interconnect system that over comes the disadvantages associated with via of the prior art PWBs.